An image forming apparatus which includes a plurality of light sources corresponding to one developing unit, and a multi-beam scanning unit configured to form an electrostatic latent image on a photosensitive member with a plurality of light beams respectively emitted from a plurality of light sources, and develops the electrostatic latent image by the developing unit has been hitherto known. In this image forming apparatus, the electrostatic latent image forming interval which is the interval between the electrostatic latent images formed on the photosensitive member with a plurality of light beams corresponding to one developing unit fluctuates due to optical errors, mechanical errors, fluctuations in optical systems by an increase in temperature, or the like, and image quality may be degraded.
Accordingly, an image forming apparatus which has a function of adjusting the electrostatic latent image forming interval has been hitherto known (see, for example, JP-A-2004-098593). Specifically, this image forming apparatus causes a multi-beam scanning unit to perform an operation to form so-called solid marks with no gap between scanning lines only by light beams from the same light source for each of a plurality of light sources. The image forming apparatus has a sensor which outputs a signal according to the positions of a plurality of marks formed on a photosensitive member, and adjusts the electrostatic latent image forming interval based on the signal from the sensor.
On the other hand, in a case where the electrostatic latent image forming interval is adjusted, the density of an image may be influenced. However, in the related art, studies have not been sufficiently done on the adjustment of the electrostatic latent image forming interval and the influence on the density of an image.